Fluidized bed furnace and waste treatment method

ABSTRACT

A waste treatment technique includes: blowing a fluidizing gas from around a mixture discharge port to form a first fluidization region having a degree of fluidization of the fluidizable particles which is set to an extent allowing waste to be accumulated on fluidizable particles, while blowing a fluidizing gas between the first fluidization region and an opposite-side wall at a higher flow velocity to form a second fluid region having a degree of fluidization of fluidizable particles greater than that in the first fluidization region, whereby the fluidizable particles are mixed with the waste to gasify the waste; and supplying waste from a supply-side sidewall portion onto the fluidized bed to cause the waste to be accumulated on the first fluidization region while causing the accumulated waste to be moved into the second fluidization region step-by-step.

TECHNICAL FIELD

The present invention relates to a fluidized bed furnace designed toheat waste in a fluidized bed formed by fluidizing fluidizable particlesto thereby extract a combustible gas from the waste, and a wastetreatment method.

BACKGROUND ART

Heretofore, as a fluidized bed furnace, there has been known one typedescribed in the following Patent Document 1. As illustrated in FIG. 9,this fluidized bed furnace comprises a furnace body 104 havingfluidizable sand (fluidizable particles) 102 in a furnace bottomsection, and an air supply section 106 for supplying air into thefluidizable sand 102 in the furnace bottom section so as to fluidize thefluidizable sand 102 to form a fluidized bed. The furnace body 104 has asidewall. The sidewall is provided with an input section 108 forinputting waste onto the fluidized bed therefrom.

In this fluidized bed furnace 100, the air supply section 106 is adaptedto supply air into high-temperature fluidizable sand 102. Consequently,the fluidizable sand 102 is fluidized in a levitated or suspended stateto form a fluidized bed. In this process, the air supply section 106 isadapted to supply air in such a manner that a fluidized state of thefluidizable sand 102 becomes approximately equalized in the entireregion of the fluidized bed so as to allow waste input from the inputsection 108 onto the fluidized bed to be entrapped inside the fluidizedbed and efficiently combusted.

Every time waste is input from the input section 108 onto thehigh-temperature fluidizable sand 102, the input waste is mixed with thehigh-temperature fluidizable sand 102 of the fluidized bed, andthermally decomposed (gasified). Consequently, a combustible gas isgenerated. For example, this combustible gas will be combusted at hightemperatures in a melting furnace in a subsequent stage.

Waste input into the fluidized bed furnace 100 is entrapped in theactive fluidized bed and combusted or gasified. In this process, everytime waste is intermittently input, combustible substances in the wasteare rapidly combusted, so that a rapid fluctuation in amount,concentration, etc., of a generated combustible gas will repeatedlyoccur. A change in the gasification reaction is largely dependent on aquantitative characteristic in supply of waste. Thus, in the case wherethere is a fluctuation in supply of waste or a qualitative change incomponents of waste, it is impossible to stably generate a combustiblegas. Particularly, when a large amount of easily combustible trash suchas paper or sheet-shaped plastic is comprised in waste, a fluctuation ofgeneration of a combustible gas becomes larger, and therefore there is aneed for stabilizing the gas generation.

For example, in the case where generated combustible gas is used for agas engine to generate electric power, if a combustible gas is generatedwith large fluctuations, it is impossible to obtain stable energy.Therefore, there is a need for further stabilizing a combustible gas tobe obtained in a fluidized bed furnace.

LIST OF PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP 2006-242454A

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a fluidized bedfurnace capable of stably obtaining a combustible gas even from wastecomprising easily combustible trash, and a waste treatment method.

According to one aspect of the present invention, there is provided afluidized bed furnace for heating waste to extract a combustible gasfrom the waste. The fluidized bed furnace comprises: fluidizableparticles making up a fluidized bed to heat the waste; a furnace bodyhaving a bottom wall supporting the fluidizable particles fromtherebelow, and a sidewall standing upwardly from the bottom wall,wherein the bottom wall has a mixture discharge port provided at aposition offset from a center position of the bottom wall in a specificdirection to discharge non-combustible substances in the waste andcarbides produced by heating of the waste, together with a part of thefluidizable particles, and an upper surface of the bottom wall isinclined to become lower toward the mixture discharge port so as tocause the fluidizable particles to fall on the upper surface of thebottom wall toward the mixture discharge port; a gas supply section forblowing a fluidizing gas from the bottom wall of the furnace body towardthe fluidizable particles to fluidize the fluidizable particles; a wastesupply section for supplying waste from a supply-side portion of thesidewall located on the same side as the mixture discharge port withrespect to the center position of the bottom wall, to a region on thefluidized bed adjacent to the supply-side sidewall portion, therebycausing the waste on the fluidized bed to be moved toward anopposite-side portion of the sidewall on a side opposite to the mixturedischarge port across the center position of the bottom wall. The gassupply section is adapted to blow the fluidizing gas from around themixture discharge port to form a first fluidization region having adegree of fluidization of the fluidizable particles which is set to anextent allowing waste to be accumulated on the fluidizable particles,while blowing the fluidizing gas between the first fluidization regionand the opposite-side sidewall portion at a flow velocity greater thanthat of the fluidizing gas to be blown in the first fluidization region,to form a second fluidization region having a degree of fluidization ofthe fluidizable particles greater than that in the first fluidizationregion, whereby the fluidizable particles is moved in a convection-likepattern and mixed with the waste to gasify the waste, and the wastesupply section is adapted to supply waste from the supply-side sidewallportion to the fluidized bed to cause the waste to be accumulated on thefirst fluidization region while causing the accumulated waste to bemoved into the second fluidization region step-by-step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a fluidized bed furnaceaccording to one embodiment of the present invention.

FIG. 2 is a horizontal sectional view of a furnace body, for explainingan introduction position of waste and an introduction position offluidizable particles in the fluidized bed furnace.

FIG. 3 is a diagram for explaining a nozzle arrangement in a bottom wallof the furnace body.

FIG. 4 is a diagram for explaining a furnace body having a reflectingportion in a front wall thereof, in a fluidized bed furnace according toanother embodiment of the present invention.

FIG. 5 is a diagram for explaining a furnace body having a guide portionin a rear wall thereof, in a fluidized bed furnace according to yetanother embodiment of the present invention.

FIG. 6 is a diagram for explaining a furnace body having a roof portionin each of front and rear walls thereof, in a fluidized bed furnaceaccording to still another embodiment of the present invention.

FIG. 7 is a diagram for explaining a furnace body comprising athermometer and an air supply section, in a fluidized bed furnaceaccording to yet still another embodiment of the present invention.

FIG. 8 is a diagram for explaining a waste supply section, in afluidized bed furnace according to another further embodiment of thepresent invention.

FIG. 9 is a schematic configuration diagram of a conventional fluidizedbed furnace.

DESCRIPTION OF EMBODIMENTS

With reference to the accompanying drawings, the present invention willnow be described based on one embodiment thereof.

A fluidized bed furnace according to this embodiment is designed to heatwaste by high-temperature fluidizable particles, to extract acombustible gas from the waste. As illustrated in FIG. 1, the fluidizedbed furnace comprises fluidizable particles 12, a furnace body 20, a gassupply section 30, a waste supply section 40, a sand circulation device50 and a carbide introduction device 60.

The fluidizable particles 12 make up a fluidized bed 14 to heat waste18, inside the furnace body 20. More specifically, the fluidizableparticles 12 are mixed with waste 18 while being heated up to a hightemperature by combustion of a part of waste components, so that thewaste 18 is gasified to generate a combustible gas. For example, thefluidizable particles 12 may be silica sand.

The furnace body 20 is configured to internally have the fluidizableparticles 12 and extract a combustible gas from waste 18 by means of thefluidizable particles 12 in a high temperature state. The furnace body20 has a bottom wall 21 supporting the fluidizable particles 12 fromtherebelow, a sidewall 22 standing upwardly from the bottom wall 21, anda combustible gas outlet portion 23 provided at an upper end of thesidewall 22.

The sidewall 22 has a rectangular tubular shape extending in an up-down(vertical) direction. Specifically, as also illustrated in FIG. 2, thesidewall 22 has a front wall (supply-side sidewall portion) 24 and arear wall (opposite-side sidewall portion) 25 which are disposed inopposed and spaced-apart relation to each other in a front-reardirection (in FIG. 2, in a right-left direction), and a pair of lateralwalls 26, 26 each connecting corresponding ends of the front wall 24 andthe rear wall 25. The lateral walls 26, 26 are disposed parallel to eachother. In other words, the furnace body 20 has a shape in plan view, inwhich a dimension in a width direction (widthwise dimension) as adistance between the lateral walls 26, 26 is equalized in the front-reardirection.

A portion (front wall) 24 of the sidewall 22 located on the same side asan aftermentioned mixture discharge port 29 with respect to a centerposition of the bottom wall 21 has a sand introduction section 27 and awaste introduction port 28. The sand introduction section 27 is designedto introduce fluidizable particles 12 into the furnace body 20, and thewaste introduction port 28 is designed to introduce waste 18 into thefurnace body 20. Further, a portion (rear wall) 25 of the sidewall 22located on a side opposite to the aftermentioned mixture discharge port29 across the center position of the bottom wall 21 has a carbideintroduction section 63. The carbide introduction section 63 is designedto introduce carbides (e.g., char) produced by heating of the waste 18,into the furnace body 20.

Specifically, the sand introduction section 27 is provided at awidthwise central region of a lower portion of the front wall 24 toallow fluidizable particles to be introduced into the furnace body 20 ina widthwise central area adjacent to the front wall 24 (see FIG. 2). Thesand introduction section 27 is provided at a height position wherefluidizable particles 12 can be input from above the fluidizableparticles 12 supported by the bottom wall 21 of the furnace body 20(fluidized bed 14), toward the fluidized bed 14 (more specifically, thewaste 18 supplied onto and accumulated on the fluidized bed 14). Basedon providing the sand introduction section 27 at the above specificposition, it becomes possible to input fluidizable particles 12 onto thewaste 18 accumulated on the fluidized bed 14. In this case, thefluidizable particles 12 serve as an ignition source to alloweasily-combustible trash in the waste 18 to be stably combusted(gasified) initially. It is to be noted that a section for inputtingfluidizable particles 12 is not limited to the front wall, but may beprovided in the rear wall 25 or the lateral wall 26.

The carbide introduction section 63 is provided at a widthwise centralregion of a lower portion of the rear wall 25 to allow carbides to beintroduced into the furnace body 20 in a widthwise central area adjacentto the rear wall 25 (see FIG. 2). The carbide introduction section 63 isprovided at a height position where carbides can be input from above thefluidized bed 14 in the furnace body 20, toward the fluidized bed 14.Alternatively, the carbide introduction section 63 may be provided at avertically intermediate height position of the fluidized bed 14. Whenthe carbide introduction section 63 is provided at the above position,the carbides are directly introduced into the fluidized bed 14. Thisallows carbides to be reliably introduced into the fluidized bed 14 andreliably gasified, although carbide is light in weight, so that, whenthe carbides are input from above the fluidized bed 14, they are apt tobe accumulated on the fluidized bed 14 and hard to be sufficiently mixedwith the fluidizable particles 12.

The waste introduction port 28 is provided in approximately the entireregion of the lower portion of the front wall 24 in the width direction.The waste introduction port 28 is provided at a height position wherewaste 18 can be pushed generally horizontally onto an upper surface ofthe fluidized bed 14 made up of the fluidizable particles 12 supportedby the bottom end 21 of the furnace body 20. In other words, the wasteintroduction port 28 is provided in such a manner that a lower endthereof is located at a position slightly higher than the upper surfaceof the fluidized bed 14.

The combustible gas outlet portion 23 is designed to discharge acombustible gas generated inside the furnace body 20. The combustiblegas outlet portion 23 has an outer diameter squeezed more than thesidewall 22, so that a duct or the like for supplying the combustiblegas obtained in the furnace body 20 to a subsequent stage, for example,a gas engine for electric power generation processes, can be connectedthereto.

The bottom wall 21 has a mixture discharge port 29 provided at aposition offset from the center position thereof in a specific directionto discharge non-combustible substances in waste 18 and carbidesproduced by heating of the waste 18, together with a part of thefluidizable particles 12. The mixture discharge port 29 has an openingextending over the widthwise entire region of the bottom wall 21. Thebottom wall 21 has an upper surface 21 a inclined to become lower towardthe mixture discharge port 29 so as to cause the fluidizable particles12 to fall on the upper surface 21 a. The bottom wall 21 in thisembodiment has a mixture discharge port 29 at a position offsetfrontwardly, and the upper surface 21 a of the bottom wall 21 extendsfrontwardly (in FIG. 1, in a left-to-right direction) at a constantdownward inclination. Specifically, the upper surface 21 a of the bottomwall 21 has an inclination angle of 15 degrees to 25 degrees withrespect to a horizontal plane. Based on providing the mixture dischargeport 29 at the above position, non-combustible substances and carbidessinking down from the waste 18 introduced from the waste introductionport 28 provided in the front wall 24, to a region on the fluidized bed14 adjacent to the front wall 24, are efficiently discharged to anoutside of the furnace body 20 therethrough. Further, non-combustiblesubstances and carbides sinking down from the waste 18 spread on thefluidized bed 14 toward the rear wall 25 while passing through thefluidized bed 14, and fall to the mixture discharge port 29 along theinclination of the upper surface 21 a of the bottom wall 21 and willreach. Thus, the non-combustible substances and carbides which have sunkdown on the side of the rear wall 25 are also discharged to the outsideof the furnace body 20 in an easy manner.

The upper surface 21 a of the bottom wall 21 is inclined to become lowertoward the mixture discharge port 29. Thus, during operation of thefluidized bed furnace 10, the fluidizable particles 12 in a region ofthe fluidized bed 14 adjacent to the upper surface 21 a are moved fromthe side of the rear wall 25 toward the front wall 24.

The gas supply section 30 is designed to blow a fluidizing gas from thebottom wall 21 toward the fluidizable particles 12 to fluidize thefluidizable particles 12. The gas supply section 30 comprises aplurality of nozzles 31 for blowing the fluidizing gas, a gas box 32 forsupplying the fluidizing gas to the nozzles 31, and a gas feeding unit33 for feeding the fluidizing gas to the gas box 32.

The plurality of nozzles 31 are installed to the bottom wall 21 inspaced-apart relation to each other in the width direction and thefront-rear direction, i.e., in a lattice arrangement. Each of thenozzles 31 is attached to the bottom wall 21 to penetrate through thebottom wall 21. In this embodiment, as also illustrated in FIG. 3, thebottom wall 21 is divided into a rear region 21 b and a front region 21c. Then, the plurality of nozzles 31 are installed to the rear and frontregions 21 b, 21 c in such a manner that the number of nozzles 31provided in the rear region 21 b becomes greater than the number ofnozzles 31 provided in the front region 21 c. It is to be noted that arelationship between the respective numbers of nozzles 31 in the rearand front regions 21 b, 21 c is not particularly limited. For example,the number of nozzles 31 in the front region 21 c may be equal to thenumber of nozzles 31 in the rear region 21 b. Alternatively, the numberof nozzles 31 in the front region 21 c may be greater than the number ofnozzles 31 in the rear region 21 b.

The gas box 32 has a box shape extending in the width direction, andserves as a header for distributing the fluidizing gas to an array ofthe nozzles 31 arranged side-by-side in the width direction in thebottom wall 21. The gas box 32 has a function of equalizing respectiveflow volumes of the fluidizing gas to be blown from the array of nozzles31 arranged in the width direction. In this embodiment, a plurality ofthe gas boxes 32 are provided on the side of a lower surface of thebottom wall 21 and arranged side-by-side in the front-rear direction.Thus, with respect to each of a plurality of the arrays of nozzles 31corresponding to respective ones of the gas boxes 32, the flow volume ofthe fluidizing gas to be blown from the array of nozzles 31 can bechanged. In this embodiment, five gas boxes 32 a, 32 b, 32 c, 32 d, 32 eare arranged side-by-side in the front-rear direction. Specifically,four gas boxes 32 a, 32 b, 32 c, 32 d are disposed on the side of therear wall 25 with respect to the mixture discharge port 29, and one gasbox 32 e is disposed on the side of the front wall 24 with respect tothe mixture discharge port 29.

The gas feeding unit 33 is designed to feed (supply) the fluidizing gasto the respective gas boxes 32. The gas feeding unit 33 is capable offeeding the fluidizing gas to each of the gas boxes 32 in a differentflow volume. The gas feeding unit 33 in this embodiment is configured tofeed the fluidizing gas to two of the gas boxes 32 adjacent to eachother in the front-rear direction, in such a manner that a flow volumeof the fluidizing gas to be fed to a rear one of the adjacent gas boxes32 becomes greater than a flow volume of the fluidizing gas to be fed toa front one of the adjacent gas boxes 32. The gas feeding unit 33 isadapted to feed only air to the respective gas boxes 32 to serve as thefluidizing gas. Alternatively, an inert gas such as nitrogen may be fedin combination with the air.

Specifically, during a normal operation of the fluidized bed furnace 10,i.e., when waste 18 is introduced into the furnace body 20 to generate acombustible gas from the introduced waste 18, the gas feeding unit 33 isoperable to cause the fluidizing gas to be blown from around the mixturedischarge port 29. In this process, the gas feeding unit 33 is operableto form a first fluidization region 15 having a degree of fluidizationof the fluidizable particles 12 which is set to an extent allowing thewaste 18 to be accumulated on the fluidizable particles 12.Concurrently, the gas feeding unit 33 is operable to blow the fluidizinggas between the first fluidization region 15 and the rear wall 25 at aflow velocity greater than that of the fluidizing gas to be blown in thefirst fluidization region 15, to form a second fluidization region 16having a degree of fluidization of the fluidizable particles 12 higherthan that in the first fluidization region 15. More specifically, asmentioned above, the gas feeding unit 33 is configured such that a flowvolume of the fluidizing gas to be fed to a rear one (e.g., the gas box32 b) of the gas boxes 32 adjacent to each other in the front-reardirection becomes greater than a flow volume of the fluidizing gas to befed to a front one (e.g., the gas box 32 c) of the adjacent gas boxes32. In this case, the gas feeding unit 33 is operable to, in thefluidized bed 14, form the first fluidization region 15 restrained influidization, around the mixture discharge port 29, while forming thesecond fluidization region 16 actively fluidized, between the firstfluidization region 15 and the rear wall 25. Alternatively, the gasfeeding unit 33 may be configured to feed the fluidizing gas to each ofthe gas boxes 32 c, 32 d, 32 e on the side of the front wall 24, in aconstant flow volume, and feed the fluidizing gas to each of the gasboxes 32 a, 32 b on the side of the rear wall 25, in a flow volumegreater than the constant flow volume. In this case, the gas feedingunit 33 is operable to, in the fluidized bed 14, form the firstfluidization region 15 restrained in fluidization, in a regioncorresponding to the gas boxes 32 c, 32 d, 32 e on the side of the frontwall 24, while forming the second fluidization region 16 activelyfluidized, in a region corresponding to the gas boxes 32 a, 32 b on theside of the rear wall 25.

Specifically, the gas feeding unit 33 is adapted to cause the fluidizinggas to be blown in the first fluidization region 15 at the flow velocitysatisfying a condition that U_(o)/U_(mf) ranges from 1 to less than 2,and blown in the second fluidization region 16 at the flow velocitysatisfying a condition that U_(o)/U_(mf) ranges from 2 to less than 5.In this formula, U_(mf) is a minimum fluidization velocity which is aminimum flow velocity of the fluidizing gas to be blown so as tofluidize the fluidizable particles 12. Further, U_(o) is across-sectional average flow velocity of the fluidizing gas.

On the other hand, during stop of the fluidized bed furnace 10, i.e.,when the introduction of waste 18 into the furnace body 20 is stopped,the gas feeding unit 33 is operable to feed a mixture formed by mixingan inert gas with air, as the fluidizing gas to be supplied to therespective gas boxes 32. Then, the gas feeding unit 33 is operable togradually increase the inert gas in a ratio between air and the inertgas in the fluidizing gas. Consequently, the gas feeding unit 33 cansuppress violent or rapid combustion of the waste 18 remaining in thefurnace body 20, thereby restraining a rise in internal temperature ofthe furnace body 20.

More specifically, during the normal operation, in the furnace body 20,combustion, gasification, etc., of the waste 18 are performed under acondition that an oxygen concentration is set to a value less than thatsuitable for combustion of the waste 18. In this state, when theintroduction of waste 18 into the furnace body 20 is stopped, an amountof combustible substances in the furnace body 20 will be reduced. Inthis process, the fluidizing gas (air) is continuously supplied into thefurnace body 20 in a predetermined flow volume to maintain the fluidizedbed 14, so that the oxygen concentration in the furnace body 20 will beincreased. When the oxygen concentration in the furnace body 20 reachesa value suitable for combustion of the waste 18 remaining in the furnacebody 20, the waste 18 is violently or rapidly combusted, so that theinternal temperature of the furnace body 20 becomes higher than thatduring the normal operation. In such a high-temperature state of theinside of the furnace body 20, the fluidizable particles 12 forming thefluidized bed 14 are agglomerated due to the heat. Once the fluidizableparticles 12 are agglomerated, even if the fluidizing gas issubsequently blown into the agglomerated fluidizable particles 12 inorder to form the fluidized bed 14, the agglomerated fluidizableparticles 12 will never be fluidized. Therefore, the gas feeding unit 33is operable, when the introduction of waste 18 into the furnace body 20is stopped, to mix an inert gas with air to be blown into the furnacebody 20, and gradually increase the ratio of the inert gas. This allowsthe oxygen concentration in the furnace body 20 to be kept at a valueless than that suitable for combustion of the waste 18. Consequently, itbecomes possible to suppress violent or rapid combustion of the waste 18remaining in the furnace body 20.

Further, the gas feeding unit 33 is adapted to be capable of adjusting atemperature of the fluidizing gas to be fed to the gas boxes 32. The gasfeeding unit 33 is operable, upon start of the operation of thefluidized bed furnace 10, to blow the fluidizing gas in a hightemperature state from a region corresponding to the second fluidizationregion 16, toward the fluidizable particles 12. In this way, the gasfeeding unit 33 is operable to heat the fluidizable particles 12 untilthe fluidizable particles 12 reach a temperature capable of performingcombustion and gasification of the waste 18. In this case, when thefluidizable particles 12 is heated up to a high temperature andcombustion of the waste 18 is started, the temperature of thefluidizable particles 12 will be maintained by the combustion. Thus, thegas feeding unit 33 may be configured to lower the temperature of thefluidizing gas to be fed to the gas boxes 32 just after start of thecombustion.

The waste supply section 40 is designed to supply waste 18 from thefront wall 24 to a region on the fluidized bed 14 adjacent to the frontwall 24. The waste supply section 40 in this embodiment is configured topush waste 18 generally horizontally from the front wall 24(specifically, the waste introduction port 28 of the front wall 24) ontothe fluidized bed 14, thereby causing the waste 18 to be moved towardthe second fluidization region 16. In other words, the waste supplysection 40 is adapted to push waste 18 to cause the waste 18 to beaccumulated on the first fluidization region 15 while causing theaccumulated waste 18 to be moved into the second fluidization region 16step-by-step. The waste supply section 40 comprises a pusher 41 and adrive unit (illustration is omitted) for driving the pusher 41. Thepusher 41 has a pushing surface 42 extending in the width direction. Inthis embodiment, the pushing surface 42 has a widthwise length equal toa width of the waste introduction port 28 of the front wall 24. Further,the pushing surface 42 has a vertical length which is approximately ahalf of a height dimension of an opening of the waste introduction port28. The pusher 41 is installed to be movable in the front-reardirection, at the same height position as that of the waste introductionport 28. The drive unit comprises a driving power source such as a motoror a cylinder, and is adapted to reciprocatingly move the pusher 41 inthe front-rear direction by the driving power. It is to be noted thatthe waste supply section 40 is not limited to a specific configuration.For example, the waste supply section 40 in this embodiment isconfigured such that the pusher 41 is employed to push waste 18 into thefurnace body. However, the waste supply section may be configured suchthat a screw extruder or the like is employed to push waste 18 into thefurnace body (see FIG. 8A). Based on employing the pusher 41 or thescrew extruder, it becomes possible to supply trash which is likely tobe scattered due to its small bulk specific gravity, such as paper orplastic sheet, into the furnace body 20 while keeping a massive form.This makes it possible to suppress scattering of trash inside thefurnace body 20, as compared to a conventional furnace in which trash isinput from an upper portion thereof.

The sand circulation device 50 is designed to separate the fluidizableparticles 12 from a mixture of the non-combustible substances, thecarbides and the fluidizable particles 12 discharged from the mixturedischarge port 29, and return the separated fluidizable particles 12 tothe inside of the furnace body 20, thereby circulating the fluidizableparticles 12. As above, according to the sand circulation device 50, thehigh-temperature fluidizable particles 12 are separated from the mixtureand returned to the inside of the furnace body 20, which makes itpossible to maintain an amount of the fluidizable particles 12 making upthe fluidized bed 14 inside the furnace body 20, and makes it easy tomaintain a temperature of the fluidized bed 14. The sand circulationdevice 50 comprises a mixture discharge section 51, afluidizable-particle separation section 52, and a fluidizable-particleconveyance section 53.

The mixture discharge section 51 is provided just below the mixturedischarge port 29 of the bottom wall 21, and adapted to move the mixtureof the non-combustible substances, the carbides and the fluidizableparticles 12 dropping from the mixture discharge port 29, to thefluidizable-particle separation section 52. The mixture dischargesection 51 in this embodiment is configured to move the mixture droppingfrom the mixture discharge port 29, to the fluidizable-particleseparation section 52 by using a screw extruder. Thefluidizable-particle separation section 52 is adapted to separate thefluidizable particles 12 from the mixture sent from the mixturedischarge section 51. The fluidizable-particle separation section 52 inthis embodiment is configured to separate the fluidizable particles 12from the mixture by using a sieve. The fluidizable-particle separationsection 52 is operable to send the mixture after subjected to theseparation of the fluidizable particles 12, to a carbide separationsection 61. The fluidizable-particle conveyance section 53 is adapted toconvey the fluidizable particles 12 separated in thefluidizable-particle separation section 52, to the sand introductionsection 27, and introduce the conveyed fluidizable particles 12 into thefurnace body 20 via the sand introduction section 27.

In this embodiment, the sand circulation device 50 is configured toinput the fluidizable particles 12 from above the fluidized bed 14toward the upper surface of the fluidized bed 14. Alternatively, thesand circulation device may be configured to return the fluidizableparticles 12 to the fluidized bed 14 in such a manner as to push thefluidizable particles 12 directly into the fluidized bed 14.

The carbide introduction device 60 is designed to separate the carbidesfrom the mixture discharged from the mixture discharge port 29, andreturn the separated carbides to the inside of the furnace body 20 fromthe side of the rear wall 25. As above, according to the carbideintroduction device 60, the carbides discharged from the mixturedischarge port 29 are returned to the second fluidization region 16,which makes it possible to obtain a combustible gas from the carbidesdischarged to outside of the furnace body 20 together with thenon-combustible substances. Consequently, a combustible gas can beefficiently obtained from waste 18 supplied to the fluidized bed furnace10. In addition, a temperature of the second fluidization region 16 canbe kept at a high value by heat generated when the carbides aregasified. The carbide introduction device 60 comprises a carbideseparation section 61, and a carbide conveyance section 62.

The carbide separation section 61 is adapted to separate the carbidesfrom the mixture sent from the fluidizable-particle separation section52. The carbide separation section 61 in this embodiment is configuredto separate the carbides from the mixture after subjected to theseparation of the fluidizable particles 12 in the fluidizable-particleseparation section 52. For example, the carbide separation section 61may be a gravity (specific gravity) separator for separating a carbidefrom a mixture by means of vibration. The carbide conveyance section 62is adapted to convey the carbides separated in the carbide separationsection 61, to the carbide introduction section 63, and introduce theconveyed carbides into the furnace body 20 via the carbide introductionsection 63.

In the fluidized bed furnace 10 configured as above, a combustible gasis collected from waste 18 in the following manner.

The gas feeding unit 33 feeds the fluidizing gas to the respective gasboxes 32. Thus, the fluidizing gas is blown from the bottom wall 21 intothe furnace body 20 toward the fluidizable particles 12, so that thefluidized bed 14 is formed inside the furnace body 20. In this process,the gas feeding unit 33 adjusts a flow volume of the fluidizing gas tobe fed to each of the gas boxes 32. Through this adjustment, in thefluidized bed 14, the first fluidization region 15 restrained influidization is formed on the side of the mixture discharge port 29, andthe second fluidization region 16 actively fluidized is formed betweenthe first fluidization region 15 and the rear wall 25. Further, the gasfeeding unit 33 feeds the fluidizing gas in a high-temperature state toa part (e.g., in this embodiment, the gas boxes 32 a, 32 b) of the gasboxes 32 corresponding to the second fluidization region 16 topositively heat the fluidizable particles 12 in the second fluidizationregion 16. Concurrently, heat is supplied to the first fluidizationregion 15 by a movement of the fluidizable particles 12 from the secondfluidization region 16 to the first fluidization region 15 which occursin a region of the fluidized bed 14 adjacent to the upper surface 21 aof the bottom wall 21 due to the inclination of the upper surface 21 a.

Subsequently, when temperatures of the regions 15, 16 in the fluidizedbed 14 formed inside the furnace body 20 reach respective predeterminedvalues (in this embodiment, the predetermined temperature of the secondfluidization region 16 is in the range of about 600 to 800° C., and thepredetermined temperature of the first fluidization region 15 is in therange of about 400 to 600° C.), the waste supply section 40 starts topush waste 18 into the furnace body 20 via the waste introduction port28. Specifically, the pusher 41 driven by the drive unit pushes waste 18generally horizontally toward the rear wall 25. Through this operation,the waste 18 is pushed onto the first fluidization region 15 at aposition adjacent to the front wall 24 (see FIG. 2).

The fluidization of the fluidizable particles 12 in the firstfluidization region 15 is restrained. Thus, the pushed waste 18 is notpositively mixed with the fluidizable particles 12, so that most of thewaste 18 is accumulated on the first fluidization region 15, and heavynon-combustible substances and a part of carbides therein sink down.Consequently, in the first fluidization region 15, rapid combustion ofthe waste 18 is suppressed, and easily gasifiable substances in thewaste 18 are gasified by heat radiation within the furnace body 20. Inother words, easily gasifiable waste 18 such as plastic or paper isgasified while being moved in a surface layer of the first fluidizationregion 15. In other words, easily gasifiable waste 18 such as plastic orpaper is gasified while being moved in a surface layer of the secondfluidization region 16. On the other hand, not-easily gasifiable wastesuch as a wood piece is partially gasified, but a large part thereofreaches the second fluidization region 16 without being gasified. Inthis manner, the easily gasifiable waste 18 is gasified under a mildcondition in the first fluidization region 15 before it reaches thehighly fluidized bed (second fluidization region 16). This makes itpossible to suppress a fluctuation of generation of the combustible gas.The heavy non-combustible substances sink down in the first fluidizationregion 15, and directly discharged from the mixture discharge port 29.This, the non-combustible substances are less likely to be accumulatedon a furnace floor. Further, in some cases, a part of the not-easilygasifiable waste such as a wood piece is also discharged from themixture discharge port 29 in a state in which it is carbonized bypassing through the first fluidization region 15. The accumulated waste18 is combusted due to the internal temperature of the furnace body 20(heat in a free board section), as mentioned above. However, althoughthe internal temperature of the furnace body 20 is in the range of 800to 900° C. which is greater than that of the fluidizable particles 12forming the fluidized bed 14, a contact between the waste 18 and air isnot satisfactory. Thus, easily combustible trash, such as paper orsheet-shaped plastic, in waste 18, is mainly gasified. In this process,the first fluidization region 15 has a relatively low temperature, andan amount of air (fluidizing gas) to be supplied to the firstfluidization region 15 is relatively small, so that even the easilycombustible trash will be gradually gasified. Further, according tofluidization of the fluidizable particles 12 caused by the fluidizinggas, a part of the accumulated waste 18 is moved or spread from thefirst fluidization region 15 to the second fluidization region 16 (inFIG. 1, in a right-to-left direction) step-by-step. Therefore, even ifwaste 18 is input in a massive form, and easily combustible papers arecomprised therein, the papers will be gasified based on a phenomenonthat the papers are moved toward a surface of the massive waste duringthe spreading. As above, in the first fluidization region 15, rapidcombustion of the waste 18 is suppressed to prevent a rapid increase ofcombustible gas during introduction of waste 18.

Subsequently, new waste 18 is pushed into the furnace body 20 via thewaste introduction port 28 by the pusher 41. Thus, the waste 18accumulated on the first fluidization region 15 is pushed by the newwaste 18, and moved into the second fluidization region 16 step-by-step.The second fluidization region 16 is actively fluidized and heated up toa high temperature by combustion of the waste 18, so that the waste 18moved from a position on the first fluidization region 15 is mixed withthe fluidizable particles 12 and sufficiently gasified. Consequently, acombustible gas is generated. More specifically, in the fluidized bed14, a fluidized state gradually becomes more active in a direction fromthe front wall 24 to the rear wall 25. Thus, when the waste 18 is movedfrom a position on the first fluidization region 15 adjacent to thefront wall 24 to the second fluidization region 16 step-by-step, it willbe gradually mixed with the fluidizable particles 12. Further, an amountof air (fluidizing gas) blown toward the fluidized bed 14 is graduallyincreased in the direction from the front wall 24 to the rear wall 25.Thus, when the waste 18 is moved from the first fluidization region 15to the second fluidization region 16 step-by-step, it will be graduallycombusted, causing an increase in temperature of the fluidizableparticles 12. In the high-temperature second fluidization region 16, thewaste 18 is sufficiently mixed with the fluidizable particles 12. Thisallows the uncombusted waste 18 remaining after passing through thefirst fluidization region 15 to be sufficiently gasified in the secondfluidization region 16.

On the other hand, the waste 18 newly pushed onto the first fluidizationregion 15 by the pusher 41 is accumulated on the first fluidizationregion 15 almost without being mixed with the fluidizable particles 12as mentioned above. Then, the accumulated waste 18 is graduallycombusted under the condition that violent or rapid combustion issuppressed.

As above, under the condition that the first fluidization region 15 andthe second fluidization region 16 are formed in the fluidized bed 14,waste 18 is pushed in one after another by the pusher 41, which makes itpossible to suppress intermittent and rapid generation of a combustiblegas, thereby stabilizing the gas generation.

The non-combustible substances and carbides which have sunk down in thefirst fluidization region 15 are discharged from the mixture dischargeport 29 provided on the underside of the first fluidization region 15,together with a part of the fluidizable particles 12. Further, thenon-combustible substances and carbides which have sunk down in thesecond fluidization region 16 are moved to the mixture discharge port 29while falling along the upper surface 21 a of the bottom wall 21,because the upper surface 21 a is inclined with a downward slope towardthe mixture discharge port 29. The moved non-combustible substances andcarbides are discharged together with a part of the fluidizableparticles 12. Then, the sand circulation device 50 separates thefluidizable particles 12 from the mixture discharged from the mixturedischarge port 29, and introduces the separated fluidizable particles 12into the furnace body 20. Concurrently, the carbide introduction device60 separates the carbides from the mixture discharged from the mixturedischarge port 29, and introduces the separated carbides into thefurnace body 20. Specifically, the mixture discharge section 51 sendsthe mixture dropping from the mixture discharge port 29 of the furnacebody 20, to the fluidizable-particle separation section 52. Thefluidizable-particle separation section 52 separates the fluidizableparticles 12 from the mixture, and the fluidizable-particle conveyancesection 53 conveys the fluidizable particles 12 separated by thefluidizable-particle separation section 52, to the sand introductionsection 27 of the furnace body 20. In this way, in the furnace body 20,an amount of the fluidizable particles 12 forming the fluidized bed 14is maintained. Further, the fluidizable-particle separation section 52sends the mixture after subjected to the separation of the fluidizableparticles 12, to the carbide separation section 61, and then the carbideseparation section 61 separates the carbides. Then, the carbideconveyance section 62 conveys the carbides separated by the carbideseparation section 61, to the carbide introduction section 63 of thefurnace body 20. This allows the carbides discharged from the furnacebody 20 together with the non-combustible substances to be returned tothe inside of the furnace body 20, and gasified. Consequently, thefluidized bed furnace 10 becomes capable of efficiently obtaining acombustible gas from waste 18.

In advance of stopping the fluidized bed furnace 10, the pushing ofwaste 18 into the furnace body 20 by the pusher 41 is firstly stopped.Upon stopping the pushing of waste 18, the gas feeding unit 33 feeds amixture formed by mixing an inert gas with air, as the fluidizing gas tobe supplied to the respective gas boxes 32. In this process, the gasfeeding unit 33 operates to gradually increase the inert gas in a ratiobetween air and the inert gas in the fluidizing gas, with time. In thismanner, the gas feeding unit 33 restrains an oxygen concentration withinthe furnace body 20 to suppress violent or rapid combustion of the waste18 remaining in the fluidized bed 14.

In this embodiment, during stop of the fluidized bed furnace 10, violentor rapid combustion of the waste 18 remaining in the fluidized bed 14 issuppressed by gradually increasing the ratio of the inert gas occupiedin the fluidizing gas. Alternatively, during stop of the fluidized bedfurnace 10, combustion of the remaining waste 18 may be prevented byspraying water onto the fluidized bed 14.

As mentioned above, the fluidized bed furnace 10 according to the aboveembodiment is capable of suppressing intermittent and rapid generationof a combustible gas to stabilize the gas generation, even in asituation where a large amount of easily combustible trash is comprisedin waste 18. Specifically, in the fluidized bed 14, the firstfluidization region 15 around the mixture discharge port 29 and thesecond fluidization region 16 having a fluidization degree higher thanthat in the first fluidization region 15 are formed. In this state, newwaste 18 is pushed onto the first fluidization region 15. The input ofthe new waste 18 causes the waste 18 accumulated on the firstfluidization region 15 to be moved toward the second fluidization region16 step-by-step. The above operation will be repeated. Thus, thefluidized bed furnace 10 can sufficiently gasify the waste 18, whilesuppressing rapid fluctuation of generation of a combustible gas.Consequently, it becomes possible to stably generate a combustible gasfrom the waste 18. In addition, just after input into the furnace body20, the waste 18 is not exposed to the highly fluidized bed (the secondfluidization region 16), so that it becomes possible to suppress asituation where a large amount of lightweight trash flies up inside thefurnace body 20 and undergoes rapid combustion in a free board section.

In addition, the first fluidization region 15 is formed just above themixture discharge port 29, and waste 18 is supplied onto the firstfluidization region 15. Thus, even if the waste 18 is accumulated on thefirst fluidization region 15, and, during a period where easilycombustible trash in the waste 18 is slowly gasified, non-combustiblesubstances and carbides sink down to a furnace bottom, suchnon-combustible substances and carbides can be easily discharged fromthe furnace body 20. Further, even when non-combustible substances andcarbides sink down to the bottom wall 21 after the waste 18 is movedfrom the first fluidization region 15 into the second fluidizationregion 16, the non-combustible substances and carbides will fall alongthe upper surface 21 a of the bottom wall 21 which is inclined to becomelower toward the mixture discharge port 29. Thus, such non-combustiblesubstances and carbides can also be easily discharged. In the secondfluidization region 16, the fluidizing gas is actively supplied. Thisalso accelerates the falling of the non-combustible substances andcarbides toward the mixture discharge port 29.

The furnace body 20 has a shape in plan view, in which a dimension inthe width direction thereof is equalized in a pushing direction of waste18. Thus, when the waste 18 on the first fluidization region 15 ispushed by waste 18 newly pushed by the waste supply section 40, andmoved toward the second fluidization region 16, the movement of thewaste 18 is stabilized.

In the waste supply section 40, the pusher 41 is adapted to bereciprocatingly moved in a direction parallel to the pushing direction(front-rear direction) to allow the pushing surface 42 to push waste 18onto the fluidized bed 14 simultaneously by the entire widthwise regionof the pushing surface 42. This allows the pushing surface 42 to pushwaste 18 onto the fluidized bed 14 with an even force in the widthdirection. Thus, the movement of the waste 18 from the firstfluidization region 15 to the second fluidization region 16 isapproximately equalized in the width direction, so that it becomespossible to prevent the waste 18 from concentrating on a certain portioninside the furnace.

It is to be understood that a fluidized bed furnace and a wastetreatment method of the present invention are not limited to the aboveembodiment, but various changes and modifications may be made thereinwithout departing from the spirit and scope of the present inventionhereinafter defined.

In the above embodiment, the sidewall 22 stands upwardly and straightfrom the bottom wall 21 to the combustible gas outlet portion 23.Alternatively, for example, as illustrated in FIG. 4, the sidewall maycomprise a front wall 24A having a reflecting portion 224 extendingtoward the rear wall 25 to cover an upper side of the first fluidizationregion 15 at a predetermined height position. The front wall 24A allowsthe waste 18 accumulated on the first fluidization region 15 to beheated by radiation heat from the reflecting portion 224. Consequently,it becomes possible to generate a combustible gas from the waste 18accumulated on the first fluidization region 15. In other words,gasification of the waste 18 accumulated on the first fluidizationregion 15 is promoted. In this case, the sand introduction section 27may be provided in the portion of the front wall 24A standing verticallyfrom the bottom wall 21, or may be provided in the reflecting portion224.

Alternatively, as illustrated in FIG. 5, the sidewall may comprise arear wall 25A having a guide portion 225 extending toward the front wall24 to cover an upper side of the second fluidization region 16 at apredetermined height position. The guide portion 225 is adapted to guidea high-temperature combustible gas generated from the waste 18 in thesecond fluidization region 16 to allow the combustible gas to be broughtinto contact with the waste 18 accumulated on the first fluidizationregion 15. In this way, the guide portion 225 allows the combustible gasto contribute to heating of the waste 18 accumulated on the firstfluidization region 15. Consequently, it becomes possible to promotegasification of the waste 18 accumulated on the first fluidizationregion 15 without adding special heating means to the furnace body 20.In this case, the carbide introduction section 63 may be provided in theportion of the rear wall 25 standing vertically from the bottom wall 21,or may be provided in the guide portion 225.

Alternatively, as illustrated in FIG. 6, the sidewall may comprise afront wall 24B and a rear wall 25B having, respectively, two roofportions 324, 325 extending in a direction causing them to come closerto each other at the same height position. The front wall 24B and therear wall 25B allow the waste 18 accumulated on the first fluidizationregion 15 to be heated by radiation heat from the roof portion 324 ofthe front wall 24B, so as to promote gasification thereof. In addition,a dimension of a furnace body 20B in the front-rear direction is reducedat a position lower than the combustible gas outlet portion 23 at theupper end of the furnace body 20B, so that it becomes possible tofacilitate a reduction in size of the furnace body 20B. In this case,the sand introduction section 27 may be provided in a portion of thefront wall 24B standing vertically from the bottom wall 21, or may beprovided in the roof portion 324. Further, the carbide introductionsection 63 may be provided in a portion of the rear wall 25B standingvertically from the bottom wall 21, or may be provided in the roofportion 325.

In the above embodiment, only carbides are introduced into the furnacebody 20 from the carbide introduction section 63. Alternatively, thecarbides may be introduced into the furnace body 20 from the carbideintroduction section 63, together with fluidizable particles 12.

In the above embodiment, the carbide introduction device 60 is adaptedto introduce the carbides separated from the mixture directly into thefurnace body 20 from the carbide introduction section 63. Alternatively,the carbides separated from the mixture may be pulverized and thenintroduced into the furnace body 20. In this case, even if carbidesdischarged from the mixture discharge port 29 are agglomerated into alarge block, the block can be pulverized into a size suitable forfacilitating gasification by heating, and returned to the furnace body20.

The upper surface 21 a of the bottom wall 21 may be curved from the rearwall 25 to the mixture discharge port 29, instead of being inclinedstraight.

As illustrated in FIG. 7, a plurality of thermometers T may be disposedjust above the first fluidization region 15, and an air supply section65 capable of supplying air onto the first fluidization region 15 may beprovided. In this fluidized bed furnace, an accumulated amount of thewaste 18 accumulated on the first fluidization region 15 can beestimated, so that it becomes possible to control the accumulatedamount. Specifically, the accumulated amount of the waste 18 on thefirst fluidization region 15 is estimated by utilizing a phenomenon thatan indication value of the thermometer T embedded in the waste 18 islowered. When the accumulated amount is relatively large, i.e., thenumber of the thermometers T embedded in the waste 18 is relativelylarge, the air supply section 65 is operable to supply air to increasean internal temperature of the furnace body 20. Accordingly,gasification of the waste 18 accumulated on the first fluidizationregion 15 is prompted, so that the accumulated amount of the waste 18 isreduced. As another method, an amount of the air may be controlled basedon determinations made as follows: when a temperature of a designatedone of the thermometers T is equal to or greater than a threshold value,it is determined that there is no waste at a position of the designatedthermometer T, and, when the temperature is less than the thresholdvalue, it is determined that there is waste at the position of thedesignated thermometer T (the designated thermometer T is embedded inwaste). Alternatively, instead of control of the amount of the air, anamount of waste to be input may be controlled.

In the above embodiment, the gas feeding unit 33 is configured to feedair and/or an inert gas as the fluidizing gas. Alternatively, forexample, the gas feeding unit 33 may be configured to feed water vaporand/or oxygen as the fluidizing gas, depending on a combustion statewithin the furnace body 20. The fluidized bed furnace 10 may furthercomprise a second gas supply section provided in the sidewall 22 inaddition to the first gas supply section 30, wherein the second gassupply section may be configured to be capable of supplying air, oxygen,water vapor or the like into the furnace body 20, depending on acombustion state in the fluidized bed 14 or of the waste 18.

The fluidizing gas to be supplied to the first fluidization region 15may be a high-temperature fluidizing gas. In the case of supplying thehigh-temperature fluidizing gas, even in a situation where it isdifficult to sufficiently keep a temperature of the first fluidizationregion 15 only by heat transferred from the second fluidization region16, the temperature of the first fluidization region 15 can bemaintained at a high value without increasing an amount of thefluidizing gas to be supplied.

In the above embodiment, the waste introduction port 28 is provided at aheight position partially overlapping with respect to the waste 18accumulated on the fluidized bed 14 in the up-down direction, so thatwaste 18 supplied from the waste introduction port 28 positively movesthe waste 18 accumulated on the upper surface of the fluidized bed 14,generally horizontally (toward the first fluidization region 15).Alternatively, the fluidized bed furnace 10 may have any configurationcapable of supplying waste 18 to a region on the fluidized bed 14adjacent to the front wall (supply-side sidewall portion) 24. Forexample, as illustrated in FIG. 8A and FIG. 8B, the waste introductionport 28 may be provided at a height position which is located adjacentto the upper surface of the fluidized bed 14, and where new waste can beintroduced in such a manner that it is placed on the waste 18accumulated on the fluidized bed 14. In this case, as illustrated, forexample, in FIG. 8A, the waste introduction port 28 may be provided toallow new waste to be supplied generally horizontally from a heightposition above the waste 18 accumulated on the fluidized bed 14.Alternatively, as illustrated in FIG. 8B, the waste introduction port 28may be provided to allow new waste to be supplied downwardly from aheight position above the waste 18 accumulated on the fluidized bed 14.Even if waste 18 is supplied into the furnace body 20 in the abovemanner, when the new waste 18 is supplied onto the accumulated waste 18,a pile of waste 18 is broken and spread, and the spread waste 18 ismoved toward the second fluidization region 16. Thus, gasification ofthe waste 18 is sufficiently performed while suppressing rapidfluctuation of generation of a combustible gas to be collected from thefluidized bed furnace 10. Consequently, it becomes possible to stablygenerate a combustible gas from the waste 18.

In the above embodiment, in a situation where non-combustible substancesare accumulated around the mixture discharge port 29 of the furnacefloor (upper surface 21 a of the bottom wall 21) without beingdischarged to the outside, the fluidizing gas may be supplied in thefirst fluidization region 15 at a flow velocity satisfying the conditionthat U_(o)/U_(mf) ranges from 2 to less than 5, only for a certainperiod of time in order to discharge the accumulated non-combustiblesubstances to the outside. In this case, preferably, an amount of thefluidizing gas to be supplied to each of the gas boxes 32 is increasedto a value greater than that during the normal operation, step-by-stepin a direction from the rear wall 25 (left side in FIG. 1) to the frontwall 24 (right side in FIG. 1) of the furnace body 20, instead ofblowing the fluidizing gas evenly in the entire first fluidizationregion 15. Based on the above operation, even if non-combustiblesubstances are accumulated around the mixture discharge port 29 of thefurnace floor during the normal operation, it becomes possible toreliably discharge the non-combustible substances to the outside of thefurnace body 20. The above specific operation is performed only for asignificantly short time, so that an influence on facilities in asubsequent stage can be minimized.

Outline of Embodiment

The outline of the above embodiment is as follows.

The fluidized bed furnace according to the above embodiment is designedto heat waste to extract a combustible gas from the waste. The fluidizedbed furnace comprises: fluidizable particles making up a fluidized bedto heat the waste; a furnace body having a bottom wall supporting thefluidizable particles from therebelow, and a sidewall standing upwardlyfrom the bottom wall, wherein the bottom wall has a mixture dischargeport provided at a position offset from a center position of the bottomwall in a specific direction to discharge non-combustible substances inthe waste and carbides produced by heating of the waste, together with apart of the fluidizable particles, and an upper surface of the bottomwall is inclined to become lower toward the mixture discharge port so asto cause the fluidizable particles to fall on the upper surface of thebottom wall toward the mixture discharge port; a gas supply section forblowing a fluidizing gas from the bottom wall of the furnace body towardthe fluidizable particles to fluidize the fluidizable particles; a wastesupply section for supplying waste from a supply-side portion of thesidewall located on the same side as the mixture discharge port withrespect to the center position of the bottom wall, to a region on thefluidized bed adjacent to the supply-side sidewall portion, therebycausing the waste on the fluidized bed to be moved toward anopposite-side portion of the sidewall on a side opposite to the mixturedischarge port across the center position of the bottom wall, wherein:the gas supply section is adapted to blow the fluidizing gas from aroundthe mixture discharge port to form a first fluidization region having adegree of fluidization of the fluidizable particles which is set to anextent allowing waste to be accumulated on the fluidizable particles,while blowing the fluidizing gas between the first fluidization regionand the opposite-side sidewall portion at a flow velocity greater thanthat of the fluidizing gas to be blown in the first fluidization region,to form a second fluidization region having a degree of fluidization ofthe fluidizable particles greater than that in the first fluidizationregion, whereby the fluidizable particles are moved in a convection-likepattern and mixed with the waste to gasify the waste; and the wastesupply section is adapted to supply waste from the supply-side sidewallportion to the fluidized bed to cause the waste to be accumulated on thefirst fluidization region while causing the accumulated waste to bemoved into the second fluidization region step-by-step.

In this fluidized bed furnace, the first fluidization region around themixture discharge port and the second fluidization region having afluidization degree higher than that in the first fluidization regionare formed in the fluidized bed. In this state, the waste supply sectionsupplies waste to a region on the fluidized bed adjacent to thesupply-side sidewall portion to cause the waste to be accumulated on thefirst fluidization region while causing the waste accumulated on thefirst fluidization region to be moved into the second fluidizationregion step-by-step. Thus, gasification of the waste is sufficientlyperformed while suppressing rapid fluctuation of generation of acombustible gas to be collected from the fluidized bed furnace, so thatit becomes possible to stably generate a combustible gas from the waste.

Specifically, in the first fluidization region, fluidization inrestrained to allow the waste to be accumulated on the upper surface ofthe first fluidization region, so that the waste is accumulated on thefirst fluidization region without being mixed with the fluidizableparticles, and easily combustible trash in the waste is slowly gasified.Therefore, in the first fluidization region, rapid combustion of thewaste is suppressed, and generation of a combustible gas caused by rapidgasification of the waste is minimized. When new waste is supplied intothe furnace body by the waste supply section, the waste accumulated onthe first fluidization region is moved into the second fluidizationregion step-by-step. In the second fluidization region, the fluidizableparticles are actively fluidized and heated to a high temperature bycombustion of the waste, so that the waste moved from a position on thefirst fluidization region is sufficiently mixed with the fluidizableparticles, and thereby the waste is sufficiently gasified to generate acombustible gas. Consequently, it becomes possible to suppressintermittent and rapid generation of a combustible gas, therebystabilizing the gas generation.

The first fluidization region is formed just above the mixture dischargeport, and waste is supplied onto the first fluidization region. Thus,even if the waste is accumulated on the first fluidization region, and,during a period where easily combustible trash in the accumulated waste18 is slowly gasified, non-combustible substances in the waste andcarbides produced by heating of the waste sink down to a furnace bottom,such non-combustible substances and carbides can be easily dischargedfrom the furnace body. Further, even when non-combustible substances andcarbides sink down to the bottom wall after the waste is moved from thefirst fluidization region into the second fluidization region, thenon-combustible substances and carbides will fall along the uppersurface of the bottom wall which is inclined to become lower toward themixture discharge port. Thus, such non-combustible substances andcarbides can also be easily discharged from the furnace body.

The upper surface of the bottom wall is inclined to become lower towardthe mixture discharge port (i.e., inclined to become lower in thedirection from the second fluidization region to the first fluidizationregion), so that the high-temperature fluidizable particles in thesecond fluidization region 16 fall on the upper surface of the bottomwall toward the first fluidization region. Consequently, heat issupplied to the first fluidization region.

Preferably, the waste supply section is adapted to push new wastegenerally horizontally from the supply-side sidewall portion toward thewaste accumulated on the first fluidization region, thereby causing thewaste accumulated on the first fluidization region to be moved into thesecond fluidization region step-by-step.

According to this feature, new waste is pushed generally horizontallytoward the waste accumulated on the first fluidization region. Thus, thewaste accumulated on the first fluidization region is pushed by the newwaste and reliably moved into the second fluidization region.

Preferably, the fluidized bed furnace comprises a carbide introductiondevice for separating the carbides from a mixture of the non-combustiblesubstances, the carbides and the fluidizable particles discharged fromthe mixture discharge port, and returning the separated carbides to thefluidized bed from the side of the opposite-side sidewall portion.

According to this feature, the carbide introduction device operates toreturn the carbides discharged from the mixture discharge port togetherwith the fluidizable particles and the non-combustible substances, tothe second fluidization region actively fluidized and highly heated.This makes it possible to obtain a combustible gas from the carbides.Consequently, the combustible gas can be efficiently obtained fromwaste. In addition, the temperature of the second fluidization regioncan be kept at a high value by heat generated when the carbides aregasified.

Preferably, in the fluidized bed furnace of the present invention, theair supply section is adapted to blow the fluidizing gas in the firstfluidization region at a flow velocity satisfying a condition thatU_(o)/U_(mf) ranges from 1 to less than 2, and blow the fluidizing gasin the second fluidization region at a flow velocity satisfying acondition that U_(o)/U_(mf) ranges from 2 to less than 5, where U_(mf)is a minimum fluidization velocity which is a minimum flow velocity ofthe fluidizing gas to be blown enough to fluidize the fluidizableparticles, and U_(o) is a cross-sectional average flow velocity of thefluidizing gas. The first fluidization region and the secondfluidization region can be desirably formed in the fluidized bed byblowing the fluidizing gas at the above flow velocities. Consequently,it becomes possible to desirably gasify the waste while suppressingrapid combustion of the waste, thereby stably obtaining a combustiblegas from the waste.

Preferably, the fluidized bed furnace comprises a sand circulationdevice for separating the fluidizable particles from the mixturedischarged from the mixture discharge port, and returning the separatedfluidizable particles to the furnace body.

According to this feature, the sand introduction device operates toreturn the high-temperature fluidizable particles discharged from themixture discharge port to the inside of the furnace body. This makes itpossible to maintain an amount of the fluidizable particles making upthe fluidized bed, and makes it easy to maintain a temperature of thefluidized bed.

More preferably, the sand circulation device is adapted to return thefluidizable particles separated from the mixture onto the wasteaccumulated on the first fluidization region.

According to this feature, the sand circulation device operates toreturn the high-temperature fluidizable particles discharged from themixture discharge port onto the waste accumulated on the firstfluidization region. Thus, the high-temperature fluidizable particlesserve as an ignition source to allow easily-combustible trash in thewaste to be stably combusted (gasified).

Preferably, the furnace body has a shape in plan view, in which adimension in a width direction perpendicular to a pushing directionalong which waste is pushed by the waste supply section is equalized inthe pushing direction.

According to this feature, when the waste on the first fluidizationregion is pushed by waste newly pushed by the waste supply section, andmoved toward the second fluidization region, the movement of the wasteis stabilized, because the dimension of the furnace body in a directionperpendicular to the waste pushing direction (width direction) isequalized.

Preferably, the waste supply section comprises a pusher having a pushingsurface extending in the width direction, and a drive unit forreciprocatingly moving the pusher in a direction parallel to the pushingdirection to allow the pushing surface of the pusher to push waste ontothe fluidized bed simultaneously by the entire widthwise region of thepushing surface.

According to this feature, waste can be pushed with an even force in thewidth direction, so that the movement of the waste from the firstfluidization region to the second fluidization region is approximatelyequalized in the width direction. Thus, it becomes possible to preventthe waste from concentrating on a certain portion inside the furnace.

The waste treatment method according to the above embodiment is designedto heat waste to extract a combustible gas from the waste. The wastetreatment method comprises: a preparation step of preparing a fluidizedbed furnace comprising fluidizable particles making up a fluidized bedto heat the waste, a furnace body having a bottom wall supporting thefluidizable particles from therebelow and a sidewall standing upwardlyfrom the bottom wall, wherein the bottom wall has a mixture dischargeport provided at a position offset from a center position of the bottomwall in a specific direction to discharge non-combustible substances inthe waste and carbides produced by heating of the waste, together with apart of the fluidizable particles, and an upper surface of the bottomwall is inclined to become lower toward the mixture discharge port so asto cause the fluidizable particles to fall on the upper surface of thebottom wall toward the mixture discharge port; a fluidization-regionformation step of blowing a fluidizing gas from a region of the bottomwall of the furnace body around the mixture discharge port toward thefluidizable particles to form a first fluidization region having adegree of fluidization of the fluidizable particles which is set to anextent allowing waste to be accumulated on the fluidizable particles,while blowing the fluidizing gas between the first fluidization regionand an opposite-side portion of the sidewall on a side opposite to themixture discharge port across the center position of the bottom wall, ata flow velocity greater than that of the fluidizing gas to be blown inthe first fluidization region, to form a second fluidization regionhaving a degree of fluidization of the fluidizable particles greaterthan that in the first fluidization region; and a gasification step ofsupplying waste from a supply-side portion of the sidewall located onthe same side as the mixture discharge port with respect to the centerposition of the bottom wall, to a region on the fluidized bed adjacentto the supply-side sidewall portion, thereby causing the waste to beaccumulated on the first fluidization region, while causing theaccumulated waste to be moved into the second fluidization regionstep-by-step and gasified.

In this waste treatment method, the first fluidization region around themixture discharge port and the second fluidization region having afluidization degree higher than that in the first fluidization regionare formed in the fluidized bed. In this state, the waste is accumulatedon the first fluidization region, and the waste accumulated on the firstfluidization region is moved into the second fluidization regionstep-by-step. Thus, gasification of the waste is sufficiently performedwhile suppressing rapid fluctuation of generation of a combustible gasto be collected from the fluidized bed furnace, so that it becomespossible to stably generate a combustible gas from the waste.

The first fluidization region is formed just above the mixture dischargeport, and waste is supplied onto the upper surface of the firstfluidization region. Thus, even if the waste is accumulated on the firstfluidization region, and, during a period where easily combustible trashin the accumulated waste is slowly gasified, non-combustible substancesin the waste and carbides produced by heating of the waste sink down toa furnace bottom, such non-combustible substances and carbides can beeasily discharged from the furnace body. Further, even whennon-combustible substances and carbides sink down to the bottom wallafter the waste is moved from the first fluidization region into thesecond fluidization region, the non-combustible substances and carbideswill fall along the upper surface of the bottom wall which is inclinedto become lower toward the mixture discharge port. Thus, suchnon-combustible substances and carbides can also be easily dischargedfrom the furnace body.

The upper surface of the bottom wall is inclined to become lower towardthe mixture discharge port (i.e., inclined to become lower in thedirection from the second fluidization region to the first fluidizationregion), so that the high-temperature fluidizable particles in thesecond fluidization region fall on the upper surface of the bottom walltoward the first fluidization region. Consequently, heat is supplied tothe first fluidization region.

Preferably, the gasification step includes pushing new waste generallyhorizontally from the supply-side sidewall portion toward the wasteaccumulated on the first fluidization region, thereby causing the wasteaccumulated on the first fluidization region to be moved into the secondfluidization region step-by-step and gasified.

According to this feature, new waste is pushed generally horizontallytoward the waste accumulated on the first fluidization region. Thus, thewaste accumulated on the first fluidization region is pushed by the newwaste and reliably moved into the second fluidization region, andgasified.

Preferably, the above waste treatment method comprises a step ofseparating the carbides from a mixture of the non-combustiblesubstances, the carbides and the fluidizable particles discharged fromthe mixture discharge port, and returning the separated carbides to thefluidized bed from the side of the opposite-side sidewall portion.

According to this feature, the carbides discharged from the mixturedischarge port together with the fluidizable particles and thenon-combustible substances are separated and returned to the secondfluidization region actively fluidized and highly heated. This makes itpossible to reliably gasify the carbides. In addition, the temperatureof the second fluidization region can be kept at a high value by heatgenerated when the carbides are gasified.

Preferably, in the above waste treatment method, the fluidizing gas isblown in the first fluidization region at a flow velocity satisfying acondition that U_(o)/U_(mf) ranges from 1 to less than 2, and blown inthe second fluidization region at a flow velocity satisfying a conditionthat U_(o)/U_(mf) ranges from 2 to less than 5, where U_(mf) is aminimum fluidization velocity which is a minimum flow velocity of thefluidizing gas to be blown so as to fluidize the fluidizable particles,and U_(o) is a cross-sectional average flow velocity of the fluidizinggas.

The first fluidization region and the second fluidization region can bedesirably formed in the fluidized bed by blowing the fluidizing gas atthe above flow velocities. Consequently, it becomes possible todesirably gasify the waste while suppressing rapid combustion of thewaste, thereby stably obtaining a combustible gas from the waste.

INDUSTRIAL APPLICABILITY

As above, the fluidized bed furnace and the waste treatment method ofthe present invention are useful in heating waste in a fluidized bedformed by fluidizing fluidizable particles, to extract a combustible gasfrom the waste, and suitable for stably obtaining a combustible gas evenfrom waste comprising easily combustible trash.

1. A fluidized bed furnace for heating waste to extract a combustiblegas from the waste, comprising: fluidizable particles making up afluidized bed to heat the waste; a furnace body having a bottom wallsupporting the fluidizable particles from therebelow, and a sidewallstanding upwardly from the bottom wall, wherein the bottom wall has amixture discharge port provided at a position offset from a centerposition of the bottom wall in a specific direction to dischargenon-combustible substances in the waste and carbides produced by heatingof the waste, together with a part of the fluidizable particles, and anupper surface of the bottom wall is inclined to become lower toward themixture discharge port so as to cause the fluidizable particles to fallon the upper surface of the bottom wall toward the mixture dischargeport; a gas supply section for blowing a fluidizing gas from the bottomwall of the furnace body toward the fluidizable particles to fluidizethe fluidizable particles; a waste supply section for supplying wastefrom a supply-side portion of the sidewall located on the same side asthe mixture discharge port with respect to the center position of thebottom wall, to a region on the fluidized bed adjacent to thesupply-side sidewall portion, thereby causing the waste on the fluidizedbed to be moved toward an opposite-side portion of the sidewall on aside opposite to the mixture discharge port across the center positionof the bottom wall, wherein: the gas supply section is adapted to blowthe fluidizing gas from around the mixture discharge port to form afirst fluidization region having a degree of fluidization of thefluidizable particles which is set to an extent allowing waste to beaccumulated on the fluidizable particles, while blowing the fluidizinggas between the first fluidization region and the opposite-side sidewallportion at a flow velocity greater than that of the fluidizing gas to beblown in the first fluidization region, to form a second fluidizationregion having a degree of fluidization of the fluidizable particlesgreater than that in the first fluidization region, whereby thefluidizable particles are moved in a convection-like pattern and mixedwith the waste to gasify the waste; and the waste supply section isadapted to supply waste from the supply-side sidewall portion to thefluidized bed to cause the waste to be accumulated on the firstfluidization region while causing the accumulated waste to be moved intothe second fluidization region step-by-step.
 2. The fluidized bedfurnace as defined in claim 1, wherein the waste supply section isadapted to push new waste generally horizontally from the supply-sidesidewall portion toward the waste accumulated on the first fluidizationregion, thereby causing the waste accumulated on the first fluidizationregion to be moved into the second fluidization region step-by-step. 3.The fluidized bed furnace as defined in claim 1, which comprises acarbide introduction device for separating the carbides from a mixtureof the non-combustible substances, the carbides and the fluidizableparticles discharged from the mixture discharge port, and returning theseparated carbides to the fluidized bed from the side of theopposite-side sidewall portion.
 4. The fluidized bed furnace as definedin claim 1, wherein the gas supply section is adapted to blow thefluidizing gas in the first fluidization region at a flow velocitysatisfying a condition that U_(o)/U_(mf) ranges from 1 to less than 2,and blow the fluidizing gas in the second fluidization region at a flowvelocity satisfying a condition that U_(o)/U_(mf) ranges from 2 to lessthan 5, where U_(mf) is a minimum fluidization velocity which is aminimum flow velocity of the fluidizing gas to be blown enough tofluidize the fluidizable particles, and U_(o) is a cross-sectionalaverage flow velocity of the fluidizing gas.
 5. The fluidized bedfurnace as defined in claim 1, which comprises a sand circulation devicefor separating the fluidizable particles from a mixture of thenon-combustible substances, the carbides and the fluidizable particles,the mixture discharged from the mixture discharge port, and returningthe separated fluidizable particles to the furnace body.
 6. Thefluidized bed furnace as defined in claim 5, wherein the sandcirculation device is adapted to return the fluidizable particlesseparated from the mixture onto the waste accumulated on the firstfluidization region.
 7. The fluidized bed furnace as defined in claim 1,wherein the furnace body has a shape in plan view, in which a dimensionin a width direction perpendicular to a pushing direction along whichwaste is pushed by the waste supply section is equalized in the pushingdirection.
 8. The fluidized bed furnace as defined in claim 7, whereinthe waste supply section comprises a pusher having a pushing surfaceextending in the width direction, and a drive unit for reciprocatinglymoving the pusher in a direction parallel to the pushing direction toallow the pushing surface of the pusher to push waste onto the fluidizedbed simultaneously by the entire widthwise region of the pushingsurface.
 9. A waste treatment method for heating waste to extract acombustible gas from the waste, comprising: a preparation step ofpreparing a fluidized bed furnace comprising fluidizable particlesmaking up a fluidized bed to heat the waste, a furnace body having abottom wall supporting the fluidizable particles from therebelow and asidewall standing upwardly from the bottom wall, wherein the bottom wallhas a mixture discharge port provided at a position offset from a centerposition of the bottom wall in a specific direction to dischargenon-combustible substances in the waste and carbides produced by heatingof the waste, together with a part of the fluidizable particles, and anupper surface of the bottom wall is inclined to become lower toward themixture discharge port so as to cause the fluidizable particles to fallon the upper surface of the bottom wall toward the mixture dischargeport; a fluidization-region formation step of blowing a fluidizing gasfrom a region of the bottom wall of the furnace body around the mixturedischarge port toward the fluidizable particles to form a firstfluidization region having a degree of fluidization of the fluidizableparticles which is set to an extent allowing waste to be accumulated onthe fluidizable particles, while blowing the fluidizing gas between thefirst fluidization region and an opposite-side portion of the sidewallon a side opposite to the mixture discharge port across the centerposition of the bottom wall, at a flow velocity greater than that of thefluidizing gas to be blown in the first fluidization region, to form asecond fluidization region having a degree of fluidization of thefluidizable particles greater than that in the first fluidizationregion; and a gasification step of supplying waste from a supply-sideportion of the sidewall located on the same side as the mixturedischarge port with respect to the center position of the bottom wall,to a region on the fluidized bed adjacent to the supply-side sidewallportion, thereby causing the waste to be accumulated on the firstfluidization region, while causing the accumulated waste to be movedinto the second fluidization region step-by-step and gasified.
 10. Thewaste treatment method as defined in claim 9, wherein the gasificationstep includes pushing new waste generally horizontally from thesupply-side sidewall portion toward the waste accumulated on the firstfluidization region, thereby causing the waste accumulated on the firstfluidization region to be moved into the second fluidization regionstep-by-step and gasified.
 11. The waste treatment method as defined inclaim 9, which comprises a step of separating the carbides from amixture of the non-combustible substances, the carbides and thefluidizable particles, the mixture discharged from the mixture dischargeport, and returning the separated carbides to the fluidized bed from theside of the opposite-side sidewall portion.
 12. The waste treatmentmethod as defined in claim 9, wherein the fluidizing gas is blown in thefirst fluidization region at a flow velocity satisfying a condition thatU_(o)/U_(mf) ranges from 1 to less than 2, and blown in the secondfluidization region at a flow velocity satisfying a condition thatU_(o)/U_(mf) ranges from 2 to less than 5, where U_(mf) is a minimumfluidization velocity which is a minimum flow velocity of the fluidizinggas to be blown so as to fluidize the fluidizable particles, and U_(o)is a cross-sectional average flow velocity of the fluidizing gas.